Browsing by Author "Neethling, P. H."

Now showing 1 - 3 of 3
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    Free charge carrier absorption in silicon at 800 nm
    (Springer, 2016) Heisel, P.-C.; Ndebeka, W. I.; Neethling, P. H.; Paa, W.; Rohwer, E. G.; Steenkamp, C. M.; Stafast, H.
    The transmission of a Ti:sapphire laser beam (c.w. and fs pulsed operation at 800 nm) through a 10-μm-thin oxidized silicon membrane at 45° angle of incidence at first increases with the incident laser power, then shows a maximum, and finally decreases considerably. This nonlinear transmission behavior is the same for c.w. and pulsed laser operation and mainly attributed to free charge carrier absorption (FCA) in Si. A simple FCA model is developed and tested.
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    Investigation of the non-linear properties and optical limiting capabilities of C₆₀ and polyfluorene
    (Academy of Science for South Africa, 2005) Neethling, P. H.; Rohwer, E. G.; Walters, P. E.
    The non-linear properties of C60 and polyfluorene were investigated using the z-scan technique. C60 is a well-known optical limiter and its non-linear properties have been measured and documented. These measurements gave us an indication of the capabilities as well as the accuracy of our own experimental setup. Preliminary absorption measurements of polyfluorene indicated an unexpected time dependence.
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    Second harmonic generation as a technique to probe buried interfaces
    (Academy of Science for South Africa, 2009) Neethling, P. H.; Scheldt, T.; Rohwer, E. G.; Von Bergmann, H. M.; Stafast, H.
    Since the advances of femtosecond laser technology during the last decade, optical second harmonic generation (SHG) has proven itself a powerful tool to investigate the electronic and structural properties of semiconductor materials. Its advantage lies in the fact that it is a contact-less, non-intrusive method that can be used in situ. It is sensitive to systems with broken symmetry, in particular interfaces and surfaces. The Si/SiO 2 system is technologically important since it forms a component of most modern electronic equipment. Furthermore, it has been shown that it is possible to induce an electric field across this Interface by means of laser irradiation as a result of defect formation and defect population. This electric field can be measured since it determines the SHG signal. The anisotropy of the SHG signal from the Sl/SiO 2 interface was measured and showed four-fold symmetry, illustrating that the SHG technique was able to characterise the electrical properties of the interface below the 5 nm thick oxide layer.